As recognized herein, projector assemblies on computerized devices have been used to project a whiteboard onto a surface. A person can ghost write onto the projected whiteboard by moving, in free space, a pen with an infrared (IR) emitter on it. The projector includes an IR detector (the detecting portion of an IR “tracker”) so that movement of the pen in free space is tracked by means of its IR emitter, and the movement is correlated to pen strokes which can then be projected onto the whiteboard, as if the person were manually writing on a physical whiteboard.
As understood herein, the IR emitter may from time to time be blocked from the IR tracker by, for instance, the user.